Radio broadcast receivers using analog-to-digital conversion of the intermediate frequency signal have been known, for example, from the disclosure of DE 29 33 416.A1. Receivers there disclosed have processor controlled phase regulation stages as well as frequency dividers for setting digital frequencies.
In the publication "UKW-Berichte 3/88" at pages 136 to 155, digital signal processing techniques for radio amateurs are described, in which, among other things, a digitalized shortwave receiver is mentioned having a frequency synthesizer which can be set in 10 kHz steps. In this receiver there is a connection of a pulse generator to this frequency synthesizer. That pulse generator provides the clock frequency for a digital signal processor (DSP) and for a central processing unit (CPU), from which a connection line leads likewise to the frequency synthesizer. The pulse generator also supplies at a 40 kHz output the sampling pulses for a 16 bit analog-to-digital converter for the intermediate frequency signal.
Broadcast receivers with digitally settable receiving frequencies are also known from German patent 29 16 171, in which the front end circuits not directly connected to the frequency synthesizer are directly tuned by the microprocessor by means of a digital-to-analog converter.
In published German Patent application P 41 04 882 an analog-to-digital conversion of an intermediate frequency signal was proposed in the form of a so-called sigma-delta converter for the conversion of an analog signal into a serial data stream of which the clock frequency had a prescribed relation to the bandwidth of the intermediate frequency signal.